Optical comparator and inspection apparatus

ABSTRACT

An optical comparator in which images of a master component and a sample component are inspected by comparison of the images that are projected in a moving, abutting, merging, mirror image, a limited area of the components being viewed in a scanning illumination at a controlled rate for full viewing coverage. The components are held in a sliding tray with means for rapidly changing the component to be inspected, while maintaining precise alignment. A closely directed light source and efficient cooling device permits prolonged operation of the apparatus, and instant access to mark defective portions of the component is provided, without interrupting viewing. The location of each defective portion is marked on a reference chart for use in a viewer which provides a composite image of the chart and component in proper registration for easy identification of the faults.

United States Patent [1 1 Kempf 1 1 OPTICAL COMPARATOR AND INSPECTIONAPPARATUS [76] Inventor: Paul S. Kempl, 703 Stratford Ct.,

Apt. 7, Del Mar, Calif. 92014 [22] Filed: Oct. 18, I971 [21] Appl. No;I90,I87

Related US. Application Data [63] Continuation-in-part of Ser. No.63,180, Aug. 12,

1970, abandoned.

Primary Examiner-William L. Sikes Attorney, Agent, or Firm-Brown &Martin 1 June 10, I975 [57] ABSTRACT An optical comparator in whichimages of a master component and a sample component are inspected bycomparison of the images that are projected in a moving, abutting.merging, mirror image, a limited area of the components being viewed ina scanning illumination at a controlled rate for full viewing coverage.The components are held in a sliding tray with means for rapidlychanging the component to be inspected, while maintaining precisealignment. A closely directed light source and efficient cooling devicepermits prolonged operation of the apparatus, and instant access to markdefective portions of the component is provided, without interruptingviewing. The location of each defective portion is marked on a referencechart for use in a viewer which provides a composite image of the chartand component in proper registration for easy identification of thefaults.

14 Claims, 22 Drawing Figures PATENTEDJUH 1 0 I975 SHEET Fig. 3

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OPTICAL COMPARATOR AND INSPECTION APPARATUS CROSS REFERENCE TO RELATEDAPPLICATION This application is a continuation-in-part of an applicationentitled Optical Comparator and Inspection Apparatus, Ser. No. 63,180,filed Aug.'l2, I970, and now abandoned.

BACKGROUND OF THE INVENTION The inspection of complex components, suchas electronic printed circuit boards, is a tedious operation requiringconsiderable observational skill. Apart from basic element by elementchecking, various techniques have been developed to accelerate theprocess. One such technique uses a blink system, in which images of amaster component and a component being checked are alternated in asuitable display in quick succession. Any discrepancies between the twoimages tend to stand out due to an apparent blinking of the area ofdifference. Careful scrutiny is required and the blinking is very tiringto the operator.

Magnified images of the components have been projected to facilitatecomparison, but extreme care in observation is necessary, and the highintensity lighting needed to project clear images causes heatingproblems. Also, in a projection system, it is difficult to mark a faultyelement without upsetting image alignment, or shutting off the apparatusto avoid possible burning of the operators fingers.

SUMMARY OF THE INVENTION In the apparatus described herein, a mastercomponent, such as a printed circuit board, and a similar component tobe inspected, are carried in a frame in precise alignment for projectionof their two images in adjacent relation, by an opaque projectionsystem, on a large viewing screen. The frame slides out of theprojection unit for loading and unloading components, and has alignmentadjusting means which maintains proper alignment of successivecomponents. A closely controlled lighting system provides a clear imageof a narrow band of each component, the frame being moved forward orbackward at a controlled rate to scan the components. Controls formotion direction, speed and image focussing are provided at theoperators position. The images thus move in synchronization and arepositioned one above the other, so that similar portions of eachcomponent can be closely compared, a small area at a time. An efficientcooling system permits prolonged operation of the apparatus andfacilitates direct access to the component being checked for markingfaulty elements. The operator can reach through a trap door with amarking device and see the actual marking operation on the viewingscreen, without the need to pull out the frame or disturb the componentalignment, and the image display is so arranged that the markingoperation does not interfere with the display.

A grid reference at the viewing screen permits location of faults on achart assigned to the particular component. After inspection, thecomponent and its chart are placed in a viewer which superimpos'es theimages; so that the faults are clearly located and identified.

The primary object of this invention, therefore, is to provide a new andimproved optical comparator and inspection apparatus.

Another object of this invention is to provide a new and improvedoptical comparator apparatus in which large images of a master componentand a component to be checked are projected in adjacent alignment andscanned over the components a small area at a time, at a controlledrate.

Another object of this invention is to provide a new and improvedoptical comparator apparatus in which faulty elements ofa component canbe marked directly by the operator while the component remains inviewing position.

A further object of this invention is to provide a new and improvedoptical comparator apparatus, in which components to be checked areeasily and quickly inserted and removed without disturbing imagealignment.

Other objects and many advantages of this invention will become moreapparent upon a reading of the following detailed description and anexamination of the drawings, wherein like reference numerals designatelike parts throughout and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of theoptical comparator unit.

FIG. 2 is a front elevation view of the unit.

FIG. 3 is an enlarged view, partially in section, of a marker pen usedwith the unit.

FIG. 4 is an enlarged sectional view taken on line 4-4 of FIG. 1.

FIG. 5 is an enlarged sectional view taken on line 5-5 of FIG. 4.

FIG. 6 is a sectional view taken on line 6-6 of FIG. 5.

FIG. 7 is an enlarged sectional view taken on line 7-7 of FIG. 2.

FIG. 8 is a sectional view taken on line 8-8 of FIG. 7.

FIG. 9 is a sectional view taken on line 9-9 of FIG. 8.

FIG. 10 is a sectional view taken on line 10-10 of FIG. 7.

FIG. 11 is a diagrammatic side elevation view of the optical system,with associated structure shown in section and broken line.

FIG. 12 is a sectional view taken on line 12-12 of FIG. 11.

FIG. 13 is a diagram of the light reflector configuration.

FIG. 14 is a diagram of an alternative optical system.

FIG. 15 is an enlarged view of the viewing screen, showing a typicalimage presentation.

FIG. 16 is an enlarged sectional view taken on line 16-16 of FIG. 2,showing marking of a faulty element.

FIG. 17 is a basic wiring diagram of the comparator unit.

FIG. 18 is a view of a typical fault recording chart.

FIG. 19 is a side elevation view, partially cut away, of an inspectionviewer to hold the chart and component.

FIG. 20 is a view taken on line 20-20 of FIG. I9.

I FIG. 2! is a view similar to FIG. 11, but showing an alternativeoptical system and the marking of a faulty component.

FIG. 22 is a front view of the viewing screen showing the imageresulting from the arrangement of FIG. 2].

DESCRIPTION OF THE PREFERRED EMBODIMENT The optical comparator iscompletely contained in a casing 10, having a front panel 12 with a backprojection type viewing screen 14 inset in the upper portion, the casinghaving a hood 16 with sides 18 which extend forwardly to shield thescreen. For added shielding, from overhead lights, a hood extension 20is attached to the top of the casing by a hinge 22 and normally restsflat on the casing to extend beyond hood 16, as in the broken lineposition in FIG. 1. When not in use the hood extension 20 can be proppedup by a leg 24 hinged on the underside thereof. The exact configurationof the casing is not critical and may vary for the purpose ofappearance.

In the lower portion of casing 10 are two spaced parallel rails 26supporting a carriage 28, which comprises a pair of longitudinal slidemembers 30 connected by cross rails 32, the slide members being slidablealong the rails 26. On top of carriage 28 is a frame 34, having a pairof cross slide members 36 which slide on cross rails 32. The rail andslide member combinations are preferably roller type elements similar todrawer slides, for smooth action. Frame 34 is manually operated and canbe pulled out through an elongated slot 38 in one side 40 of the casing10. The carriage 28 is driven by a motor 42, having a friction driveroller 44 which rides on one slide member 30, the motor having speed andreversing controls described in more detail hereinafter.

Frame 34 has a pair of side bars 46 and 48 fixed to opposite ends ofslide members 36 to form a rigid rectangular frame. The outside bar 46,which is normally exposed in slot 38, is provided with a handle 50 tofacilitate sliding the frame in and out of the casing. At opposite endsof side bars 46 and 48 are threaded traverse rods 52 and 54, journalledin the side bars and extending parallel to slide members 36. On theinside ends of the traverse rods 52 and 54 are bevel gears 56, the tworods being interconnected by a connecting shaft 58 rotatably mounted inbearings 60 on side bar 48 and having bevel gears 56. Traverse rod 52projects outwardly from side bar 46 and is fitted with a knob 64, sothat both traverse rods can be rotated in synchronization. The traverserod 52 is oppositely threaded from the center out and a pair of traverseblocks 66 and 68 are threaded on the opposite ends. Traverse rod 54 issimilarly threaded and carries a pair of traverse blocks 70 and 72.Fixed between the traverse blocks 66 and 70 is a channelled track 74,and fixed between traverse blocks 68 and 72 is a similar track 76. Whenknob 64 is turned, the tracks 74 and 76 are moved toward or away fromeach other in parallel relation.

Slidably mounted in tracks 74 and 76 are two pairs of clamp blocks 78and 80, having inwardly opposed fingers 82 to grip the corners of arectangular master component 84, which rests on top of the tracks. Eachtrack has a longitudinal slot 86 and the clamp blocks are secured frombelow by any suitable screw of clamp means. As shown, the component 84is a simple rectangular board used for a printed circuit, but the clampblocks could be arranged to hold any other configuration. In normal use,the master component is fixed at one end of the frame between the trackswhich are ad justed to the proper width by means of knob 64, and is leftin that position until all sample components of that type have beenchecked. A sample component 88 rests on tracks 74 and 76 at the otherend of frame 34 and is held between stop blocks 90 and 92 and adjustableclamp blocks 94 and 96. Stop blocks 90 and 92 have inwardly opposedspring fingers 100, against which the 5 sample component is held byfingers 102 on the clamp blocks 94 and 96.

Below track 74 is a nut 104 fixed to clamp block 94 through slot 86, thenut running on a threaded rod 106 supported between traverse block 70and a bearing 108 10 under the center portion of the track. A similarnut and threaded rod adjustment means is coupled to clamp block 96 belowtrack 76. The threaded rods 106 extend through the supporting traverseblocks 70 and 72 and are fitted with bevel gears I10. The traverseblocks 15 have forwardly extending flanges 112, through which passes ashaft 114, journaled at its ends in side bars 46 and 48. Shaft 114 isshown as being square in cross section, but could be suitably splined,and at each traverse block 70 and 72 is a bevel gear 116 meshing withthe 20 adjacent bevel gear 110. Bevel gears 116 rotate with shaft 114but are slidable thereon to allow for adjustment in the spacing of thetracks. Shaft 114 projects from side bar 46 and is provided with a knob118, by which the clamp blocks 94 and 96 can be simulta- 25 neouslyadjusted to hold the sample component 88.

35 The top of the lamp house comprises a reflector 122 of cylindricalform extending across the full width of the carriage structure. It iswell known that light from a source at one focal point of an ellipticalreflector will be concentrated at the other focal point of the ellipse.As shown in FIG. 13, the reflector 122 in arcuate cross section isclosely similar to the section of a pair of overlapping ellipses 124 and126 with a common focal point 128, the arcuate form being simple tomanufacture. Spaced below reflector 122 is a secondary reflector 45 130of inverted V-configuration, the apex of which has an arcuately concaveportion 132. A tubular lamp 134 is mounted at the effective common focalpoint of reflector and the center of radius of concave portion 132 isspaced below the lamp, so that light reflected from the concave portionwill pass to the side of the lamp and strike the primary reflector. Theinclined walls of the secondary reflector subtend an angle of less than90, so that light is reflected at a shallow an- 5 gle, as in FIG. 11. Alarge percentage of the light is thus concentrated through the opensides 136 of the lamp house, to the areas of the components immediatelyadjacent to the lamp house. If additional light is needed, a second lamp138 may be mounted above the concave 0 portion 132, as indicated inbroken line in FIG. 11.

To provide adequate cooling, a duct 140 from a suitable blower, notshown, is led into the plenum chamber 142 formed under the secondaryreflector 130. The plenum chamber has a bottom panel 144 with slottedoutlets 146 formed by flanges 148 spaced from and parallel to the loweredges of the inclined walls. Additional slotted outlets 150 are providednear the center to increase airflow. It has been found that this type ofairflow, directed downwardly and outwardly in a thin sheet across thesurface of each component, has the greatest cooling effect and allowsprolonged operation without excess heating.

Mounted above the illuminated portion of the master component 84 is awide angle projection lens 152, above which is an inclined mirror 154 toreflect the image to the upper portion of screen 14. Above theilluminated portion of sample component 88 is a similar lens 156,directing light to a first mirror 158 above the optical path of themaster component image. First mirror 158 is inclined to direct lightdownwardly to a second mirror 160, which directs the image to the lowerportion of the screen 14. By using a single mirror for one image and twomirrors for the other, an upright image of the sample component is seenwith an inverted and effectively mirror image of the master component.As the carriage 28 is moved, the two images converge or diverge with aflowing motion, depending on the direction of motion. The correspondingends of the components and their images are marked 0 and X forreference. To obtain a sharp line of separation between the images andavoid confusing overlap, a shield or stop 162 is fixed to the lower rearedge of secondary reflector 130. Another stop 164 is secured to aplatform 166 fixed in the forward portion of the casing immediatelyabove the frame 34.

An alternative optical system, which may be desirable for some purposes,is shown in FIG. 14, in which both images are upright and move in acommon direction. The optical path for the sample component is asdescribed above, but the lens 152 over the master component 84 directsthe light to a first mirror 168 and a second mirror 170 to provide anupright image. In either form the two optical paths are of equal lengthto ensure images of matching size.

The lenses are suspended from a supporting plate 174, or comparablestructure, mounted in any suitable manner in casing 10. Lens 156, whichis a mounted cylindrical unit of conventional type, slides vertically ina sleeve 176 fixed in plate 174, the lens extending through a mountingbar 178 and being pivotally attached thereto between lugs 180, as inFIGS. 8 and 9. One end of the mounting bar 178 is held on a threadedpost 182 extending downwardly from plate 174 and biased away from theplate by a spring 184, a large adjustment nut 186 on the post below themounting bar providing for vertical adjustment. The other end ofmounting bar 178 is held on another threaded post 188 extendingdownwardly from plate 174 and spaced therefrom by a spring 190. Belowthe mounting bar is a pulley 192, which is threaded on post 188. Sincethe lens is guided and held in vertical axial alignment by sleeve 176and pivotally attached to mounting bar 178, the bar need not be parallelto plate 174, and one or both ends can be adjusted as hereinafterdescribed.

The mounting of lens 152 shown in FIG. 10, is the same in all respects,except that the adjustment nut 186 is replaced by a lock nut 194, sinceadjustment at both ends is not necessary for both lens mountings.

Pulleys 192 are coupled together by an endless belt or cord 196, wrappedaround the pulleys for positive drive, the cord extending to a controlpulley 198 mounted on a bracket 200 on front panel 12. A focussing wheel202, fixed to control pulley 198, protrudes through the front panel 12,so that the operator can turn the wheel and adjust the focus of bothlenses equally. Adjustment nut 186 is used for initial adjustment toequalize image sizes and normally does not need to be changed once set.

In initially setting up the apparatus, it may be necessary to shift oneimage laterally for precise registration. To do this, mirror 154 ismounted in a frame 204, which has a pivotal connection 206 at one end toa support member 208 fixed in casing 10, as in FIGS. 11 and 12. On theother end of frame 204 is a bracket 210, an adjustment screw 212 beingfitted through support member 208 and threaded into the bracket. Aspring 214 between bracket 210 and support member 208 maintains thesetting.

Longitudinal adjustment of the sample component to obtain properregistration of the images is made by positioning of the stop blocks and92 on their respective tracks. With a sample component in place, thefinal precise adjustment is made by turning knob 118, the spring fingersallowing limited longitudinal movement of the sample component, whileretaining a holding grip against the clamp. blocks.

In the inspection of printed circuit boards it may be desirable tocompare a sample board with a negative or transparency of the printedcircuit layout. For this purpose, backlight lamps 216 are mounted undercarriage 28, below the position of the normally illuminated portion ofthe master component, as in FIG. 11. A diffuser 218 is placed above thelamps for even lighting and the transparency is secured in the mastercomponent position. To shut off the light and heat from the lamp house,a shutter 220 is pivotally mounted in the rear portion of the lamphouse, to swing up and close the open end, as in the broken lineposition. When not in use, the shutter serves as a portion of thesecondary reflector 130, or could be made removable.

In the wiring diagram shown in FIG. 17, a power supply is connectedthrough a main switch 222 to the lights and blower of the lamp house.The backlight circuit is separately controlled through a switch 224 anddimmer 226 for balancing the image intensities when used. Motor 42 isenergized through a direct current speed control 228, such as a siliconcontrolled rectifier circuit of well known type, and has a reversingswitch 230 with a center off position. Limit switches 231 and 232 aremounted in suitable positions in the casing to limit the travel of thecarriage. The reversing switch and a knob 233 for the speed control aremounted on a recessed control panel 234 in front panel 12, and are shownpositioned for convenient one handed operation. The main switch and thebacklight controls can be at any convenient location.

A typical image presentation is shown in FIG. 15 in which it can be seenthat the sample in the lower image has a reversed polarity capacitor 236and an incorrect transistor 238, when compared to the master. Tofacilitate marking the faulty elements, front panel 12 is provided witha large trap door 240 hinged at its lower edge by a spring loaded hinge242 to swing inwardly and down on top of platform 166, the spring hingeholding the trap door closed. It has been found that marking is bestdone with a water based fluorescent ink dispensed from a squeeze typepen 244 with a long thin nozzle 246. The operators arm is pushed throughtrap door 240, as in FIG. 16, and a drop of ink is placed on the faultycircuit element. Since the marking operation can be seen on the screen,the action is quick and simple and, with the effective cooling system,the operator is in no danger of being burned. if necessary the platform166 can have a covering of thermal insulation of low reflectivity, suchas black velvet or flocking.

Several pens 244, with different colored inks, are

conveniently stored in a rack 248, mounted on front panel 12 below thetrap door. To avoid clogging of the nozzle by dried ink, each pen has acap 250 lined with resilient material 252, such as silicone rubber witha central socket 253 which is a tight fit for nozzle 246. When the capis pushed over the nozzle, the air trapped in socket 253 forces the inkback down the nozzle by a pumping action and seals the nozzle to preventclogging by dried ink.

ln another optical system, see P10. 21, mirrors 303 and 300 direct thelight image of component 88 to the upper portion of the screen 14.Mirror 302 directs the image of component 84 to the lower portion of thescreen 14. Thus as the carriage 28 is moved, the two images provide anabutting merging mirror, image display of the illuminated portions ofcomponents 84 and 88. However the center edge of the forward component88 is opposite the forward edge of the component. Thus it is possible toinsert the market pen 244 into the display to mark the defectivetransistor 306 with market dye 308, without having the hand of the userobstruct the display, see FIG. 22.

For close inspection of small details, an inspection lens 254 isslidably mounted on a rod 256 extending across hood 16, the lens beinghinged to swing upward clear of the screen when not in use, as in FIG.2.

To make a complete inspection record and facilitate identification offaults, a grid system is used. The lower edge of screen 14 is numberedfrom left to right, as in FIG. 15, and vertical reference is provided byletters spaced along track 76, as shown in FIG. 4, so as to be visiblein the image. A record is made on a printed form 258, with a grid 260corresponding to the grid of the image. Thus the chart is marked at gridpositions D3 and Fl4, to indicate the faulty elements. At the side ofform 258 is a fault table 262 of typical faults, and a line is drawnfrom each marked position on the grid to the appropriate fault, as shownin FIG. 18, to facilitate later correction. The form 258 is scaled tothe actual size of the grid in relation to the component itself, so thatby superimposing the form on the component, the markings fall over thefaulty elements. To simplify inspection, the form is placed on thebacklighted window 264 of a viewer 266. Inclined forward of the windowis a beam splitter mirror 268 and a platform 270 on which the faultysample component is placed. From a suitable viewing direction, indicatedby arrow 272 of FIG. 19, the composite images of the component and formare seen in the beam splitter mirror. Lamp 274 may be provided with adimmer to balance the image intensities.

The faulty sample component 88 rests on a fixed stop 276 in verticalalignment with the form 258, lateral alignment being set by anadjustable stop 278 against one edge of the component. Stop 278 is heldby a suitable clamp screw 280 through a transverse slot 282 in platform270. By this means, a relatively unskilled operator can correctlyindentify faults, and a record of each component is provided.

When it is not desired to mark a component then the grid system can beused separately to indicate a fault. This allows the faults to berecorded even though the test procedure does not allow marking thecomponents directly.

A single operator can set up the apparatus and inspect componentsquickly, the sample component being changed by pulling out the frame byhandle 50, lifting out the sample just checked and inserting the next,then pushing in the frame. With components assembled, on a productionbasis, there should be little if any need for adjustment of the imageeach time a component is changed. lmage motion is under full control ofthe operator and can be stopped instantly when a fault is detected, orfor careful scrutiny. The adjustment means incorporated in the componentcarrying frame will accommodate a variety of types and sizes of printedcircuit boards or other components.

Having described my invention, I now claim:

1. An optical comparator and inspection apparatus for comparing a samplecomponent with a master component by comparing respective images thereofcomprising,

a single rear projection viewing screen,

carriage means including a carriage being slidable longitudinally fromfront to rear for supporting a sample component and a master componentin spaced relation adjacent said screen,

said carriage means including positioning frame means for fixedlypositioning the sample component and reference component in a commonplane on said carriage, a light source, means for focusing light fromsaid light source onto the surface of respective similar portions of thesample component and the master component,

optical projection means including a lens and mirror system for eachcomponent for receiving light images reflected from the surface of eachof the re spective components and directing the light im ages, with oneof the images inverted, to a common point of focus on the screen inabutting relationship with one component image being a mirror image at agiven demarkation line of the other component image,

light stop means for simultaneously limiting the light images to commonlines of demarkation on each component,

and moving means for moving the sample component and reference componenton said positioning frame means and carriage means simultaneously in thecommon plane in a direction perpendicular to the optical axis of therespective lens and mirror systems on an axis longitudinal to a linebetween the optical centers of the two respective lens and mirrorsystems and past the light source and light stop means, whereby the twoimages converge and diverge from the lines of demarkation on the screen.

2. Apparatus according to claim 1 and including,

said moving means including a drive motor coupled to said carriagemeans,

speed and direction reversing means for controlling the operation ofsaid motor and the movement of the carriage means,

and said frame means includes a frame that is transversely slidable onsaid carriage means.

3. Apparatus according to claim 2, wherein,

said frame has a pair of longitudinal tracks between which thecomponents are held,

clamp elements adjustably and movably mounted on said tracks, withportions for engaging opposite edges of the components,

and said tracks have means for adjusting the spacing therebetween.

4. Apparatus according to claim 3, wherein,

said clamp elements have adjustment means for limited longitudinaladjustment of the position of the sample component relative to themaster component,

and stop element means secured on said tracks with resilient portionsfor holding sample component against said movable clamp elements.

5. Apparatus according to claim 1, wherein,

said light focusing means has a downwardly directed reflector extendingtransversely across said carriage means, the cross section of saidreflector being substantially arcuate and closely equivalent to that ofa pair of overlapping ellipses with a com mon focus,

said light source being mounted at the effective position of the commonfocus,

a secondary reflector spaced below said first reflector and definingoutwardly and downwardly directed opposed openings for directing lightin a line across transverse strip areas of the components,

and said secondary reflector has a cross section substantially ofinverted V-shape, the apex portion being arcuately concave with a centeror radius spaced below the effective common focus of the firstreflector.

6. Apparatus according to claim 1, and including,

backlighting means mounted below said carriage means at the position ofthe illuminated portion of the master component,

and said light stop means including a light shield selectively movableto obstruct the light from said light source to the master component.

7. Apparatus according to claim 1, including,

a casing for enclosing the carriage means and components, said screenbeing mounted on the frong side of said casing,

and said front side has a trap door therein providing access to theilluminated portion of the sample component.

8. Apparatus according to claim I, wherein,

said optical projection means includes a lens adjustably mounted aboveeach component, and at least one mirror for each lens mounted to directan image from each lens individually to a portion of said screen,

and focusing means coupled to said lenses with control means forfocusing both lenses simultaneously.

9. Apparatus according to claim 8, wherein,

one of said lenses has additional focusing means independent of saidcoupled focusing means.

10. Apparatus according to claim 8, wherein,

one of said mirrors has adjustable mounting means movable to shift oneimage laterally on said screen.

11. Apparatus according to claim 8, wherein,

said mirrors are arranged to project one image above the other, with oneimage inverted relative to the other.

12. Apparatus according to claim 8, wherein,

said mirrors are arranged to project one image above the other, withboth images upright.

13. Apparatus according to claim 8, and including,

said stop means being fixed above the illuminated portions of thecomponents to limit the illuminated areas correspondingly and provide asharp separation of the images projected on the screen.

14. Apparatus according to claim 1, and including,

position identifying grid means at said screen,

an inspection record form having a corresponding grid thereon on whichthe positions of faulty components are marked,

an illuminated viewer having means for holding an inspection record formand the associated sample component, and providing superimposed imagesthereof in registration.

1. An optical comparator and inspection apparatus for comparing a samplecomponent with a master component by comparing respective images thereofcomprising, a single rear projection viewing screen, carriage meansincluding a carriage being slidable longitudinally from front to rearfor supporting a sample component and a master component in spacedrelation adjacent said screen, said carriage means including positioningframe means for fixedly positioning the sample component and referencecomponent in a common plane on said carriage, a light source, means forfocusing light from said light source onto the surface of respectivesimilar portions of the sample component and the master component,optical projection means including a lens and mirror system for eachcomponent for receiving light images reflected from the surface of eachof the respective components and directing the light images, with one ofthe images inverted, to a common point of focus on the screen inabutting relationship with one component image being a mirror image at agiven demarkation line of the other component image, light stop meansfor simultaneously limiting the light images to common lines ofdemarkation on each component, and moving means for moving the samplecomponent and reference component on said positioning frame means andcarriage means simultaneously in the common plane in a directionperpendicular to the optical axis of the respective lens and mirrorsystems on an axis longitudinal to a line between the optical centers ofthe two respective lens and mirror systems and past the light source andlight stop means, whereby the two images converge and diverge from thelines of demarkation on the screen.
 2. Apparatus according to claim 1and including, said moving means including a drive motor coupled to saidcarriage means, speed and direction reversing means for controlling theoperation of said motor and the movement of the carriage means, and saidframe means includes a frame that is transversely slidable on saidcarriage means.
 3. Apparatus according to claim 2, wherein, said framehas a pair of longitudinal tracks between which the components are held,clamp elements adjustably and movably mounted on said tracks, withportions for engaging opposite edges of the components, and said trackshave means for adjusting the spacing therebetween.
 4. ApparatusaccordinG to claim 3, wherein, said clamp elements have adjustment meansfor limited longitudinal adjustment of the position of the samplecomponent relative to the master component, and stop element meanssecured on said tracks with resilient portions for holding samplecomponent against said movable clamp elements.
 5. Apparatus according toclaim 1, wherein, said light focusing means has a downwardly directedreflector extending transversely across said carriage means, the crosssection of said reflector being substantially arcuate and closelyequivalent to that of a pair of overlapping ellipses with a commonfocus, said light source being mounted at the effective position of thecommon focus, a secondary reflector spaced below said first reflectorand defining outwardly and downwardly directed opposed openings fordirecting light in a line across transverse strip areas of thecomponents, and said secondary reflector has a cross sectionsubstantially of inverted V-shape, the apex portion being arcuatelyconcave with a center or radius spaced below the effective common focusof the first reflector.
 6. Apparatus according to claim 1, andincluding, backlighting means mounted below said carriage means at theposition of the illuminated portion of the master component, and saidlight stop means including a light shield selectively movable toobstruct the light from said light source to the master component. 7.Apparatus according to claim 1, including, a casing for enclosing thecarriage means and components, said screen being mounted on the frongside of said casing, and said front side has a trap door thereinproviding access to the illuminated portion of the sample component. 8.Apparatus according to claim 1, wherein, said optical projection meansincludes a lens adjustably mounted above each component, and at leastone mirror for each lens mounted to direct an image from each lensindividually to a portion of said screen, and focusing means coupled tosaid lenses with control means for focusing both lenses simultaneously.9. Apparatus according to claim 8, wherein, one of said lenses hasadditional focusing means independent of said coupled focusing means.10. Apparatus according to claim 8, wherein, one of said mirrors hasadjustable mounting means movable to shift one image laterally on saidscreen.
 11. Apparatus according to claim 8, wherein, said mirrors arearranged to project one image above the other, with one image invertedrelative to the other.
 12. Apparatus according to claim 8, wherein, saidmirrors are arranged to project one image above the other, with bothimages upright.
 13. Apparatus according to claim 8, and including, saidstop means being fixed above the illuminated portions of the componentsto limit the illuminated areas correspondingly and provide a sharpseparation of the images projected on the screen.
 14. Apparatusaccording to claim 1, and including, position identifying grid means atsaid screen, an inspection record form having a corresponding gridthereon on which the positions of faulty components are marked, anilluminated viewer having means for holding an inspection record formand the associated sample component, and providing superimposed imagesthereof in registration.